The present invention relates to a seal mechanism used in a submersible pump and, more particularly, to a lubrication oil retaining apparatus capable of effectively cooling the sliding surface of a shaft seal device disposed within an oil chamber of the seal mechanism.
In a conventional submersible pump, a seal mechanism is provided between a pump casing and a motor chamber. In general, in consideration of expansion of lubrication oil stemming from heating-up of the sliding surface of a shaft seal device and heating-up of a motor during rotation, lubrication oil is charged into the oil chamber of the seal mechanism in an amount such that the lubrication oil occupies 80% the overall volume of the oil chamber and thus air-reserving space is formed at the upper portion of the oil chamber.
However, when the shaft seal device is rotated, the lubrication oil flows in a vortex toward the inner circumferential wall of the oil chamber due to centrifugal force generated by the rotation of the shaft seal device, and an air-reserving space is formed at the center portion of the oil chamber. As a result, the sliding surface of the shaft seal device to be lubricated comes into an unimmersed state, resulting in deterioration of the function for lubricating and cooling the sliding surface.
In view of the foregoing, a structure as shown in FIGS. 7 to 9 has been proposed as a measure for maintaining lubrication at the sliding surface of the shaft seal device.
The proposed structure will be described. A cylindrical wall member 110 is disposed to surround a shaft seal device 111. Baffle plates P for directing the flow of oil toward the center axis are disposed on the inner circumferential surface of the cylindrical wall member 110. The lower end portion of the cylindrical wall member 110 is separated from a pump-side housing 102a in order to form an oil inlet 113b along the entire circumference of the lower edge, to thereby establish communication with an oil chamber 103. The upper end portion of the cylindrical wall member 110 is fixed to the lower surface of a motor-side housing 101a. A plurality of oil outlets 113a are formed in the cylindrical wall member 110 at appropriate positions above a sliding surface 112a between an upper mating ring 105a and a seal ring 106a.
However, the results of an experiment show that when the above-described structure in which the oil inlet 113b for communication with the oil chamber 103 is formed by the entire circumference of the lower edge of the cylindrical wall member 110, centrifugal force is produced in the vicinity of the oil inlet 113b due to rotation of the double-type shaft seal device 111, so that lubrication oil within the cylindrical wall member 110 is forced to the outside, thereby greatly hindering the action of sucking and pushing the lubrication oil up.
Furthermore, employment of the above-described structure provides negative effects such that the lubrication oil scatters outward from the plurality of oil outlets 113a formed in the upper portion of the cylindrical wall member 110, with the result that the sliding surface 112a between the upper mating ring 105a and the seal ring 106a is not immersed in the lubrication oil. In addition, the scattered oil tends to entrap air in an air-reserving space 115 above an oil surface 114.
Moreover, since the amount of the lubrication oil flowing out of each oil outlet 113a changes depending on position, air is taken into the cylindrical wall member 110 via an oil outlet 113a from which a smaller amount of oil flows as compared with the remaining oil outlets 113a. This taken air, together with the action of the baffle plates P for directing oil toward the center axis against the above-described centrifugal force, hinders circulation of the lubrication oil within the cylindrical wall member 110, due to its stirring action. In addition, the lubrication oil and the air are intermixed, and thus fine bubbles are generated. As a result, a mixture of the oil and air reaches the sliding surface 112a between the upper mating ring 105a and the seal ring 106a, resulting in a decrease in the lubricating effect. Further, the flow of the lubrication oil between the inside and outside of the cylindrical wall member 110 becomes turbulent, and this turbulent flow of the lubrication oil, together with the mixing of the lubrication oil and air, drastically reduces the efficiency in cooling the sliding surface 112a. 
Moreover, although the size and number of the oil outlets 113a must be matched with the rotational speed of a pump shaft 104, in actuality, varying the size and number of the oil outlets 113a in accordance with variation in the rotational speed is impossible at a site where the submersible pump is used.
An object of the present invention is to provide a lubrication oil retaining apparatus for a submersible pump, which apparatus prevents lubrication oil from scattering from the center portion of the oil chamber of a seal mechanism toward the circumferential wall, and which circulates the lubrication oil smoothly to thereby effectively lubricate and cool the sliding surface of the shaft seal device, irrespective of variation in rotational speed of a pump shaft and without causing the entrapment of air into the lubrication oil.
The present invention provides an apparatus for retaining lubrication oil at the sliding surface of a shaft seal device disposed within an oil chamber of a submersible pump. Within the oil chamber located between a motor chamber and a pump chamber, an upper mating ring of a double-type shaft seal device is fitted into an annular groove formed on the lower surface of a motor-side housing, and a lower mating ring of the double-type shaft seal device is fitted into an annular groove formed on the upper surface of a pump-side housing. An annular holding plate for preventing rotation of the lower mating ring is fixed to the upper surface of a circumferential wall surrounding the annular groove. A cylindrical wall member is disposed to surround the double-type shaft seal device. A guide vane is fixed to the inner circumferential surface of the cylindrical wall member, the guide member having a slanted surface that inclines upward toward the rotational direction of a pump shaft. An outwardly-projecting lower edge flange is provided at the lower edge of the cylindrical wall member and fixed to the upper surface of the holding plate. A lateral hole serving as an oil inlet and establishing communication between the back side of a lower end portion of the guide vane and the oil chamber is formed in the lower portion of the cylindrical wall member. An inwardly-projecting flange is provided at the upper edge of the cylindrical wall member located above a sliding surface between the upper mating ring and a seal ring, such that the flange is in close proximity to the motor-side housing. An oil outlet is formed between the upper surface of the flange and the lower surface of a circumferential wall which surrounds the annular groove into which the upper mating ring is fitted. Preferably, the clearance between the upper surface of the flange provided at the upper edge of the cylindrical wall member and the lower surface of the circumferential wall which surrounds the annular groove into which the upper mating ring is fitted is set to fall within a range of about 0.5 mm to 3 mm; and the clearance between the inner circumferential surface of the flange provided at the upper edge of the cylindrical wall member and the outer circumferential surface of the upper seal ring is set to fall within a range of about 1 mm to 3 mm.
Preferably, a guide plate is provided at the oil inlet or the oil outlet, which is an annular clearance, in order to improve the lubrication and cooling action.